Problem on electric field due to dipoles

The black dots at the ends of the square in the figure represent charges -q or +q and they are denoted + or - by the symbol next to the them.
Now that line is drawn from the centre of the square to point P and is distance x
The side of the square is 2a

Show that Electric Field at P for x >> a is 3 (2qa^2) / 2 pi epsilon0 x^4